An exemplary Private Network Node Interface (PNNI) Asynchronous Transfer Mode (ATM) network 101 is shown in FIG. 1. ATM is a networking technology that transports information with “cells” of data. As such, if a significantly sized body of information (e.g., a document or file) is to be transported across an ATM network, the body of information is effectively “broken down” into a plurality of cells. The plurality of cells are then individually sent across the network and reassembled at the receiving end in order to reconstruct the original body of information.
The term “connection” or “circuit” is often used to describe a pre-defined path through a network. Typically, when a body of information is to be transported over a network, a connection is setup beforehand that establishes (in some manner and to some extent) the path that the cells will take. Various types of connections may be used within an ATM network 101. These include: 1) permanent virtual circuits (PVCs); 2) switched virtual circuits (SVCs); and 3) soft permanent virtual circuits (SPVCs).
In the case of PVCs, a quasi-permanent connection is established (e.g., a connection that lasts for days, weeks, months, etc.). PVCs are often used in situations where a large corporate user desires to permanently clear a guaranteed pipe through the network 101 from one large office to another large office. For example, if node 1051 corresponds to the Customer Premise Equipment (CPE) of a first corporate office and node 1052 corresponds to the CPE of a second corporate office, a PVC may be established that couples nodes 1021, 1024, 1027 and network lines 1033, 10311 together (in order to form an end-to-end path through the network 100 between CPEs 1051 and 1052).
Generally, the amount of traffic (e.g., as between two large corporate offices) and the extent of the usage (e.g., every business day for the foreseeable future) justifies the costs associated with dedicating, in a quasi-permanent fashion, a fixed amount of the network's resources to one particular pathway. Typically, a PVC is manually configured by a network manager from a network management control station 104. As such, commands are issued from the network control station 104 to the various nodes in the network 101 that “make up” the PVC (so that the lookup tables, etc. within these nodes can be properly updated).
Another characteristic of a PVC is that a PVC user simply directs traffic into the network 101 (e.g., from node 1051) with little or no formal request for transportation services from the network 101. For example, typically, a PVC user at node 1051 will send ATM cells having the PVC's VPI/VCI across the ATM User Network Interface (UNI) at link 1031. Based upon the VPI/VCI information, node 1021 (e.g., as well as subsequent nodes along the PVC path) will be able to properly switch the cells onto a link that corresponds to the PVC path. Thus, because the connection is quasi-permanent and has already been established, there is little or no procedural overhead associated with connection setup (such as a SETUP request message and the like). The user is provided an appropriate VPI/VCI well beforehand (e.g., shortly after PVC setup) which is invoked each time thereafter by the user when the services of the PVC are desired.
SVCs, on the other hand, are established on a temporary basis rather than a quasi-permanent basis. SVCs efficiently utilize the resources of a network if the network has to support a large number of different connection paths over a fairly brief period of time (e.g., seconds, minutes, hours). In contrast to PVCs, SVCs are usually established on a “call-by-call” basis and therefore have: 1) some form of formal user request to the network 101 for transportation services; and, 2) a connection “setup” procedure that follows the request for transportation services and a connection “tear down” procedure that follows the successful performance of the requested transportation services.
The connection setup/tear down procedures may be viewed as the “automatic” configuration of a connection within the network rather than manual configuration from a network management control station 104. PNNI is a routing and signaling protocol that determines and establishes connection paths. The PNNI routing protocol is executed on the source endpoint (e.g., source endpoint 1021 for connections initiated from originating node 1051), and is often referred to as a “source” routing protocol. An example of PNNI's routing and signaling techniques are provided immediately below.
If node 1051 (the “originating” node) desires to send information to node 1052 (the “target” node), the originating node 1051 will effectively request the network 101 for a connection to be established between nodes 1051 and node 1052. Typically, this request takes the form of a SETUP message that is passed over the ATM UNI at link 1031. The access node 1021 (which may be referred to as the source endpoint node) receives the SETUP message and determines an appropriate path for the connection through the network via the PNNI routing protocol.
The SETUP message then traverses the network 101 to the destination endpoint node 1027. When the SETUP message is received at the destination endpoint node 1027, a CONNECT message is issued from the destination endpoint node 1027 to the source endpoint node 1021. The CONNECT message “bounces”, node-by-node, along the connection path to the source endpoint node 1021. Each node that receives the CONNECT message updates its lookup table (or other routing/switching platform) with an appropriate reference to the connection being established. When the source endpoint node 1021 receives the CONNECT message, the VPI/VCI for the connection is passed to the user at the ATM UNI (along link 1031), the connection is established, and transportation services may commence. After the transportation services are complete, the connection is torndown in a manner similar to that in which it was established.
An SPVC is often viewed as a blending of an SVC and a PVC. SPVCs are often used to provide guaranteed bandwidth to a particular user (such that the user enjoys service as if a permanent pipe has been established through the network 101) while, simultaneously, the network 101 is allowed to flexibly adapt to different connection paths over brief periods of time (by establishing each SPVC communication with connection setup and tear down procedures). In order to implement an SPVC service, the endpoint nodes of the ATM network 101 (e.g., source node 1021 and destination node 1027) are configured to behave like PVC nodes with respect to the user (e.g., along the ATM UNI at link 1031) while behaving like SVC nodes within the ATM network 101 itself.
With an SPVC, the source and destination endpoint nodes 1021 and 1027 are usually manually configured by the network management station 104 to provide a PVC interface to the users at node 1051 (and at node 1052). That is, for example, a quasi permanent VPI/VCI is provided to the user that is to be invoked each time the services of the SPVC are desired. Upon the receipt of ATM cells having this VPI/VCI information, however, the endpoint source node 1021 triggers the release of a SETUP message which traverses the network 101 to destination endpoint node 1027. A CONNECT message is returned to the endpoint source node 1021, and the SPVC is established.